Flow channel for zigzag classifiers



April 8, 1969 w, KMSER 3,437,202

FLOW CHANNEL FOR ZIGZAG'CLASSIFIERS Filed April 4, 1967 Ill/1 Fig. 5

INVENTOR.

Fritz W. Kaiser ATTORNEYS.

United States Patent FLOW CHANNEL FOR ZIGZAG CLASSIFIERS Fritz W.Kaiser, Hammel, near Augsburg, Germany, as-

signor to Alpine Aktiengesellschaft, a company of Germany Filed Apr. 4,1967, Ser. No. 628,497 Claims priority, applicafi5on0(82;rmany, Apr. 6,1966, 2

Int. 01. B071) 7/12, 3/12 U.S. Cl. 209136 8 Claims ABSTRACT OF THEDISCLOSURE BACKGROUND OF THE INVENTION Field of the invention Thismaterial referes to a flow channel which conveys the material to beclassified into a rising-tube classifier, particularly into a zigzagclassifier, forwarding it in transverse direction to the risingclassifying fluid stream, that ascends substantially from the bottom ofsaid channel. As the fines are continuously carried out upwards, only amore or less clean coarse grain portion remains at the end of the flowchannel.

The term flow channel indicates, as generally known, mostly slightlyinclined channels, wherein dust fluidized by air blown in, is conveyedby gravity, this condition of dusts being named flow-bed. If operated inconnection with a rising-tube classifier said flow-bed has to performthe following functions at a time:

(1) Conveying, in a channel 0.8 m. wide, very considerable amounts ofmaterial, which, under certain circumstances, may be as large as 200tons per hour.

(2) Breaking-up of agglomerates or grains sticking together, whileconveyed on the channel, with a view to obtaining a clean coarseprod-uct.

(3) Regular distribution of the required volume of classifying air overthe entire separating area.

(4) Throwing at least the limit grains and fines upwards to a heightwhere they are allowed to come into contact with the uniform classifyingcurrent that is initiated only on a certain level above the layer ofmaterial so that the fines are carried upwards by said current, whereasthe coarse grains are dropped again.

Description of prior art Already known is the flow channel with a porousbottom through which air is blown, which channel conveys very largeamounts of material, the volume of air, however, not being suflicient toachieve a clean coarse product and to perform good classification. Forthis reason it has already been suggested in German patent applicationNo. A 47,159 to blow the required air through laterally arrangedauxiliary nozzles into such a channel, their influence, however, beingtoo irregularly distributed over the channel width.

In the known Vibro-Classifier the channel bottom consists of a screenwith a hole width of -1-2 mm., blown through by air from below. Toassist the conveying movement the screen is vibrated, but the flexiblesuspension Patented Apr. 8, 1969 as well as the sealing required involveconsiderable extra cost.

Screen holes must be small so as to prevent heavy grains of materialfrom falling through. The emanating air jets are, therefore, too faintto produce an eflicient breaking-up of agglomerates. (Kirchberg,Aufbereitung bergbaulicher Rohstoffe, Gronau, January 1953, page 169.)

Vibration of the screen can be substituted, as already done in theso-called pulsating classifiers (ibid., page by pulsation of the aircurrent. However, these classifiers did not give any better results.

Due to the low air velocities produced in the sieve holes of a sievesurface normally provided with about 40% of open area, both classifiertypes give a sharpness of separation which is not satisfactory.

During the initial periods of flow-bed construction, larger holes hadbeen used. However, it had not been recognized that, with an adequatelysmall open area in the sieve surface, the condition of the flying bed,as contemplated by the present invention, is obtained or that it wouldprove useful in separation processes.

In contrast with the foregoing prior structures, it is an object of thepresent invention to find a configuration of the flow-bed involving notonly the accomplishment of the afore-mentioned four functions, but alsosimplicity and cheapness.

Problems and solutions (1) There are a multitude of conditions in whicha flow-bed may occur (see, e.g., VDI Forschungshaft 509/ 1965). Optimumseparation is achieved by a flow-bed condition not described as yetatleast in connection with this particular applicationhere named flyingbed, in which the flow-bed is so largely flufled-up, for instance, to50100% of the bed volume, that considerable distances are covered by thesingle grains wirled forward in free flight, chiefly in verticaldirection. The flow-bed has no longer the otherwise known properties ofliquids as it is, for instance, exempt from floating bodies. If puttingthe hand in the bed, one feels no longer the resistance of inertiacharacteristics of liquids, but only the repeated shocks or impacts ofthe individual grains, the condition resembles the movement of moleculesof gas. It differs from that of dust conveyed in flight by the fact thatin the flying bed an equal amount of material is, on average, carriedforward in the same and in the opposite direction to the flow of thecurrent, whereas all of the material conveyed in flight is substantiallymoved forward in the current direction. Frequent collisions occur in theflowbed between the grains and especially between the grains and thebottom of the flow channel so that an eflicient breakup of agglomeratesis obtained.

For producing a flow-bed the bottom of the channel must be provided withindividual nozzles through which air is introduced and which are sodesigned that the emanating jets carry the grains of the flow-bed. Toaccomplish this purpose, two conditions must be fulfilled as follows.

(a) The jet diameter must at least be of the same dimensional order asthe grain, rather be larger so as to ensure that the single grains aresuspended by the jets without requiring the pressure-consuminginitiation of a jet velocity higher than the speed needed according tocondition (b).

(b) The impetus of the jets must be so high that they are able to keepall of the grains in suspension. From this condition results theequation:

channel bottom, 5 the density of air and AP the pressure drop at thescreen, converted to jet velocity. If v =3m./sec. of air velocity andAP=100 mm. WG, G/F would be 15 kg./m. as permissible charge in thechannel; thus, the feed rate would be rather small. This requires a jetvelocity of 40 m./sec. and an open sieve area of 7.5%. The test confirmsapproximately this equation, that does not, however, give any definitelimits for the initiation of the flow-bed.

The flow-bed condition is easy to check either visually or by puttingthe hand in and to adjust by a pressure drop large enough in relation tothe level of material, such adjustment possibly requiring adaptation ofthe open sieve area in the channel bottom.

(2) The small charge in the flow channel, the importance of which isemphasized in the preceding section, requires, with large throughlputrates a high velocity of conveyance. The invention contemplates severalmeans to achieve this speed rate.

For the initiation of the flow bed conditions immediately behind thebeginning of the flow-bed, the invention equally provides several means.

The goal aimed at is attained according to the inven tion by operationof the flow-bed in flying bed condition. As described before,adjustments to obtain said conditions can easily be made duringoperation.

For producing the flow-bed, the flow channel bottom comprises a platewherein several nozzles are fitted, this plate being most simplydesigned as a perforated sheet provided with round or otherwise shapedholes. I

Precondition of the flow-bed condition is that the individual jets arestrong enough to carry the single grains. This is mostly achieved byproviding a perforated bottom with holes the diameter of which is equalto or larger than the diameter of the largest grains conveyed. A fewoversize grains in the material are negligible.

The necessary impetus of the jets is obtained by calculating the numberof holes and the open sieve area, respectively, in such a way that thepressure drop at the perforated bottom corresponds at least to theequation:

Explication of the symbols are given above.

To keep G/F small, that means, to keep the layer of material thin, arelatively high velocity of the material being conveyed is required.This can be achieved by one or several of the following measures: M ostessential is a certain inclination of the channel; a minimum inclinationof 9 has proven eflicient.

Another feature is to make the individual air jets inclined in flowdirection. Even to avoid any braking effect on the flow of material,they must have a forward component of a value at least equal to the flowspeed of the material. A larger forward component exerts a propellingaction. These oblique jets are produced by nozzles inclined in directionof conveyance. Regarding the large number of nozzles, a low-costmanufacture is mandatory. This can easily be achieved by deforming theholes of the perforated sheet, subsequently, for instance, by pushingthrough a mandrel or when punching the holes.

In order to obtain a high velocity of the material in the channel, thisvelocity must already exist at the entry of material. This speed is mostsimply imparted to the material by a gravity chute with deflection indirection of conveyance prior to feeding the material into the channel.Dependent on flow speed, the height of fall provided by this chute mayvary from a few decimeters up to a few meters.

Since the initiation of the flow-bed, with no especial expedients,requires a certain amount of time and a certain distance on the flowchannel, it is essential to make special provisions to obtain,immediately at the beginning of the flow channel, at least part of saidflow-bed. It is already known to introduce at this point a larger amountof air through one or several enlarged nozzles arranged 4 immediatelybehind the intake. They can be spaced regularly across the channel widthor concentrated at individual spots in order to effect a splitting ofthe film of material emanating from the gravity chute.

The same purpose is accomplished by means of perturbing bodies fitted onthe bottom of the gravity channel immediately in front on the intake.They can be arranged so as to either break-up the film of material intoseveral strands or throw-up the material for mechanical initiation ofthe flow-bed.

With certain materials it has been found that, independent of any lengthof the flow channel, a dwell time of about 1 second, during which thematerial is retained in the flow channel, is required and suflicient toobtain a clean separation. With other products this period of time maybe different, notwithstanding, it is characteristic of a large varietyof materials, particularly of the iron ore Minette.

In case of a rising-tube classifier which is not free of internalstructures above the flow channel, but sub-divided into several smalltubes, especially zigzag tubes, it is es sential to provide above saidflow channel a defined headroom. Too small a headroom makes it diflicultfor the non-entrapped material to fall again out of the classifying tubeso that material would accumulate inside the tubes. With too large aheadroom, on the other hand, the flow-bed would not extend to the tubesso that the latter would be fed with an amount of material not largeenough to allow them to be utilized completely. From experience, aheadroom of 70-200 mm., reaching to any existing subdivisions of therising tube or tubes of the classifier should be provided.

In order to increase the flow speed in the channel, it is of assistanceto make the lower end portions of the rising-tube subdivisions, alsocalled aprons, to face the direction of flow. For better adaptation tothe service conditions that, under certain circumstances, require aheadroom variable along the flow-bed length, it is advantageous to makethe length of the aprons adjustable.

Should the rate of material flowing through be too large or the flowspeed be too low to operate a flow-bed all over the sieve area, it maybe helpful to set up small single flow-beds at least in the voids aroundthe individual perturbing bodies regularly spaced on the channel bottom.

Since one cannot avoid that; for instance, when shutting-down or iftemporary overloads occur, material falls through the holes in theperforated plate, it would sometimes be advisable to build in the spacebeneath the plate a worm conveyor or any other conveying means thatdischarges the fallen material, which is most simply carried out througha swing flap into the coarse product line.

Cleanness of the coarse product is increased by extending the flowchannel beyond the classifying chamber towards the coarse product side.This effect is particularly obtained by a flow path of the fines-ladenair in counterdirection to the stream of coarse product so that finesthat may be precipitated again are settling down in front of the spotwhere they have been whirled up, thus, they are given the chance ofbeing whirled up once again.

With a very small open sieve area, it may be advantageous to provide aporous sieve surface so as to prevent the fine material from settlingdown between the individual nozzles.

It has shown that, when classifying materials containing very fine orsticky dust, the sieve surface adds to the tendency of the material toform deposits under as well as on the sieve. To eliminate thisinconvenience, it has proven efficient to provide a flexible suspensionof the sieve and to tap it, at certain intervals of time, with acompressed air device of any known design. Also other knocking orshaking means are likely to prove more or less successful. The rapperpresents the advantage that the flexible suspension of the sieve can berather rigid and, therefore, inexpensive.

SUMMARY OF INVENTION The invention covers improvements in rising-tubeclassifiers and more particularly to a flow channel therefor, comprisingthe features described above, for conveying material to be classified atan incline downwardly across the classifier, the flow channel comprisinga perforated plate provided with air flow nozzles pointing in thedirection of flow and the other features associated therewith arrangedto provide for a clean separation of fines from clean coarse material.

BRIEF DESCRIPTION OF THE DRAWING An embodiment of the invention is shownby way of example on the drawing in which:

FIG. 1 is a sectional diagrammatic view showing in elevation the flowchannel arranged beneath the tubes of a rising-tube zigzag classifieraccording to the invention;

FIG. 2 is a plan view of the flow channel taken on the line IIII of FIG1;

FIG. 3 is a broken sectional view on a large scale of the perforatedplate and its nozzle structure;

FIG. 4 is a detail view showing the arrangement of a compressed-airrapper; and

FIG. 5 is a detail view of a flexible suspension means for a perforatedbottom plate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The essential parts of theclassifier as shown in FIG. 1, are the zigzag shaped rising tubes 1, ofwhich only the lower portion is shown, the flow channel 2 conveying thematerial to be classified in transverse direction to the possiblyupwardly ascending air current. The material to be classified is fed atpoint A into gravity chute 3, wherein it attains a certain velocity.Deflection part 4 of the channel bottom 5 directs it subsequently ontothe perforated bottom of the flow channel on which it is carried forwardat rather high speed until the coarse product G leaves the classifier atthe end of the flow channel through coarse product duct 6. Theclassifying air, produced by a suitable pneumatic installation, entersthrough a flanged pipe socket 7 into a distributing box 8, passesthrough bottom plate 5, ascends into the zigzag tubes 1 and, laden withthe classified fines, it is discharged at the top of the tube unit 1 tobe freed from dust in another pneumatic installation such as a cycloneseparator.

The number and size of holes in the bottom 5, which, in correlation withthe volume of air, determine the pressure differential at the perforatedplate 5, as well as the level where classification takes place and whichis dependent upon the quantity and velocity of the material beingseparated are matched so as to obtain the flow-bed condition of thematerial in the channel. The material is constantly flung upwards andlifted to the classifying tubes 1, which, according to their separationboundary, carry all of the fines they can entrap upwards so that, attheend of the flow-bed, only a more or less clean coarse product G remains.

In order to speed-up initiation of the flow-bed at the inlet end of thechannel 2, several protruding bodies 11 are arranged at the end 9 of thegravity chute 3 to subdivide the film of material into several strandsor streams between which the thickness of the layer is so small that thematerial can be immediately whirled up. A similar purpose isaccomplished by air flow slot 10 provided at the inlet end of theperforated bottom 5 and acting as a nozzle through which a strong jet ofair blows upwards. Should the layer of material, while following itspath in the flow channel, be too thick to provide a flowbed, the lattercan, at least locally, be obtained in the voids around the individualbodies 11.

The drawing indicates different means to impart to the material a highflow velocity: Bottom 5 is inclined by the angle 12, a high rate of fallis imparted to the material by gravity chute 3; the lower portions ofzigzag tubes 1 have the aprons 13 inclined in flow direction so as togive the non-entrapped material falling down a certain forward componentof velocity; the individual nozzles in the perforated bottom 5 areinclined in forward direction so as to give the issuing jets a forwardcomponent of impetus. The headroom 14 above the flow channel is solargely dimensioned that only a very small portion of the forwardimpetus is destroyed by the impact action of aprons 13 against which thewhirled-up ma terial is flung.

The inclination of the nozzles in the perforated bottom 5 is, as shownon FIG. 3, achieved in a simple manner by deforming the holes 15 in anormal perforated plate 5 with the aid of a mandrel 16 pushed throughholes 15 to bend the forward edge down. If high wear is expected, ashape like that of hole 17 may prove advantageous.

The flow channel 5 is extended by measure or amount 18 beyond the end 19of the rising tube or tubes. The air escaping from 5 in the space 18travels a certain distance in counter-direction to the stream ofmaterial which it frees, in a very eflicient manner, from the finesentrapped, without requiring any additional channel surface or extraair. The same may be achieved to a certain extent by an air flow opening22, so that air flows upwardly through the coarse material in duct 6.

Should material fall through the relatively large holes 15 in theperforated bottom 5, when stopping or if temporary overloads occur, itis directed by worm conveyor 20 and swing flap 21 into the coarseproduct duct 6.

FIG. 4 shows the arrangement of a known type of compressed-air rapper orvibrator 26, the interior design of which corresponds to that of apneumatic hammer. This rapper taps bedplate 27. To fasten it, the upperend of bottom 5 passes through the rear side of the air distributing box8, stiffened by means of welded-on straps 23 and connected to flange 24carrying plate 27 of rapper 26. The passage zone is sealed with softrubber sections 25.

FIG. 5 illustrates a structure for arranging the lengthwise, flexiblesuspension of the perforated bottom 5. Since, due to the high impactfrequency of the rapper, the vibration paths are short, said suspensionmay be rather rigid. Here, the perforated sheet 5 is interposed betweenthree soft rubber sections 28.

The measures as contemplated by the invention present, singly and incombination, the advantage that the rising-tube classifiers,particularly zigzag classifiers of the special design incorporating aflow channel allowing large feed rates to be handled and to be separatedcleanly. The equipment needed to achieve this is inexpensive and verysimple. The example below shows the results obtained.

Example Minette was separated, with 30% residue on a 315 micron sieve ina rising-tube classifier similar to that of FIG. 1, having a crosssection of 0.8 m. and being subdivided into ten classifying zigzagtubes. The flow channel, 500 mm. wide, had an inclination of 9 and wasfiltted with a perforated bottom with alternately ar ranged holes of 8and 10 mm. diameter, 13% of the total sieve area being open. Thepressure drop at these holes was about 70 mm. water gauge. Feeding 10tons per hour, the fines yield was 6.2 tons per hour with 5% residue ona 315 micron sieve; 81% of the product smaller than 315 microns enteredthe fines fraction. A classification could still be achieved at a feedrate of 40 tons per hour, with the fines yield being correspondingsmaller.

Regardless of the fact that, in the foregoing description, air wasconsitently used as the operating fluid of the classifier, any other gasor steam may be used; also warm air for drying as operating fluid may beused. If

7 the usual provisions are made for the use of liquids, the flow channelcan be operated with them.

What is claimed is:

1. In a rising-tube classifier of the type including a zigzagrising-tube unit, a flow channel extending laterally across the unit forconveying material to be classified, means for supplying material ontoone end of the flow channel, a discharge duct evacuating coarse materialat the other end of the flow channel, and means for deliveringclassifying medium to the classifier to flow up through the flow channeland the material thereon, wherein the improvement comprises aflow-channel including a perforated bottom plate provided withindividual air-flow nozzles, the diameter of the nozzles and thepressure drop therein being so rated that the individual jets from saidnozzles are strong enough to carry the single grains of said materialalong and upwardly.

2. A classifier as claimed in claim 1, wherein the airflow nozzles inthe perforated bottom plate are at least as large as the largest grainsof material to be classified.

3. A classifier as claimed in claim 2, wherein means additional to saidair-flow nozzles is provided for increasing the initial rate of flow ofmaterial on the inlet end of the flow channel 4. A classifier as claimedin claim 1, wherein means additional to said air-flow nozzles isprovided for increasing the initial rate of flow of material on theinlet end of the flow channel.

5. A classifier as claimed in claim 4, wherein said increasing meanscomprises at least one enlarged nozzle (10).

6. A classifier as claimed in claim 4, wherein said increasing means isa steeply down-inclined gravity chute (3) the bottom of which isdeflected at its lower end in the direction of the channel givingvelocity to the material as it flows onto the flow channel.

7. A classifier as claimed in claim 1, wherein said rising tube unitincludes a series of rising tubes, and wherein a headroom (14) of to 200mm. is provided reaching from the bottom plate of the flow-channel toany existing subdivision of any rising tube of the classifier.

8. A classifier as claimed in claim 7, wherein the flow channel extendsbeyond the last tube of the series where it adjoins the discharge chute.

References Cited UNITED STATES PATENTS 187,193 2/1877 Stanley 2095061,720,861 7/1929 Stebbins 209139 X 2,106,027 1/1938 Guest 209-506 X2,258,789 10/ 1941 Morgan 209504 X 2,279,590 4/ 1942 Haworth 2094662,743,817 5/1956 Musgrave et al. 209474 2,815,858 12/1957 Rich 209138FOREIGN PATENTS 380,196 9/ 1932 Great Britain. 1,014,723 12/ 1965 GreatBritain.

969,075 7/1949 Germany.

TIM R. MILES, Primary Examiner.

U.S. Cl. X.R.

